Commit 20ff51a3 authored by Colin Cross's avatar Colin Cross Committed by Len Brown
Browse files

cpuidle: coupled: add parallel barrier function 



Adds cpuidle_coupled_parallel_barrier, which can be used by coupled
cpuidle state enter functions to handle resynchronization after
determining if any cpu needs to abort.  The normal use case will
be:

static bool abort_flag;
static atomic_t abort_barrier;

int arch_cpuidle_enter(struct cpuidle_device *dev, ...)
{
	if (arch_turn_off_irq_controller()) {
	   	/* returns an error if an irq is pending and would be lost
		   if idle continued and turned off power */
		abort_flag = true;
	}

	cpuidle_coupled_parallel_barrier(dev, &abort_barrier);

	if (abort_flag) {
	   	/* One of the cpus didn't turn off it's irq controller */
	   	arch_turn_on_irq_controller();
		return -EINTR;
	}

	/* continue with idle */
	...
}

This will cause all cpus to abort idle together if one of them needs
to abort.

Reviewed-by: default avatarSantosh Shilimkar <santosh.shilimkar@ti.com>
Tested-by: default avatarSantosh Shilimkar <santosh.shilimkar@ti.com>
Reviewed-by: default avatarKevin Hilman <khilman@ti.com>
Tested-by: default avatarKevin Hilman <khilman@ti.com>
Signed-off-by: default avatarColin Cross <ccross@android.com>
Signed-off-by: default avatarLen Brown <len.brown@intel.com>
parent 4126c019

drivers/cpuidle/coupled.c

+37 −0
Original line number Diff line number Diff line
@@ -129,6 +129,43 @@ static DEFINE_PER_CPU(struct call_single_data, cpuidle_coupled_poke_cb); 
 */

static cpumask_t cpuidle_coupled_poked_mask;



/**

 * cpuidle_coupled_parallel_barrier - synchronize all online coupled cpus

 * @dev: cpuidle_device of the calling cpu

 * @a:   atomic variable to hold the barrier

 *

 * No caller to this function will return from this function until all online

 * cpus in the same coupled group have called this function.  Once any caller

 * has returned from this function, the barrier is immediately available for

 * reuse.

 *

 * The atomic variable a must be initialized to 0 before any cpu calls

 * this function, will be reset to 0 before any cpu returns from this function.

 *

 * Must only be called from within a coupled idle state handler

 * (state.enter when state.flags has CPUIDLE_FLAG_COUPLED set).

 *

 * Provides full smp barrier semantics before and after calling.

 */

void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a)

{

	int n = dev->coupled->online_count;



	smp_mb__before_atomic_inc();

	atomic_inc(a);



	while (atomic_read(a) < n)

		cpu_relax();



	if (atomic_inc_return(a) == n * 2) {

		atomic_set(a, 0);

		return;

	}



	while (atomic_read(a) > n)

		cpu_relax();

}



/**

 * cpuidle_state_is_coupled - check if a state is part of a coupled set

 * @dev: struct cpuidle_device for the current cpu

include/linux/cpuidle.h

+4 −0
Original line number Diff line number Diff line
@@ -183,6 +183,10 @@ static inline int cpuidle_play_dead(void) {return -ENODEV; } 


#endif



#ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED

void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a);

#endif



/******************************

 * CPUIDLE GOVERNOR INTERFACE *

 ******************************/

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